Overvoltage protection for transformers



Feb. 19, 1952 M. G. LEQNARD ET AL 2,586,354

OVERVOLTAGE PROTECTION FOR TRAN'SFORMERS Filed April 2v, 195o INVENTORSMerrill G. Leonard En Guy Y. Hoger.

ATTOR EY Patented Feb. 19, 1952 OVERVOLTAGE PROTECTION FOR TRANSFORMERSMerrill G. Leonard, Sharon, and Guy Y. Hager, Sharpsville, Pa.,assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application April 27, 1950, Serial No.158,396

1 Claim.

The present invention relates to overvoltage protection fortransformers, and more particularly to an improved mounting andarrangement l of a lightning arrester and high-voltage terminal meansfor protected or surge-proof transformers. or other enclosed electricaldevices.

Transformers of the protected or surge-proof type are protected againstlightning surges, or

other overvoltages such as may be caused by bushings in the tank wall.The terminal bushing must be provided with a terminal device forccnnecting a line lead to the transformer, and it must be arranged topermit vconnection of the lightning arrester to the transformer lead.

Lightning arresters of the expulsion type are usually used on protectedtransformers. In arresters of this type, when a surge is discharged, anarc is formed in an arcing chamber lined with, or containing, materialcapable of evolving substantially un-ionized gas in the presence of anarc. When a discharge occurs, a large quantity of un-ionized gas is thusevolved and is expelled through a vented electrode, deionizing the arcpath and blowing out the arc to interrupt the power current which tendsto flow to ground following the surge. An external series spark gap isalways used with lightning arresters of this type to isolate thearrester from the line under normal voltage conditions. so that theline-to-ground voltage will not be continuously applied across thearrester, and when the arrester is connected to the transformer lead onthe outside of the transformer tank, provision must be made for a seriesgap. Open gaps are objectionable, however, because exposed live parts,either of the gap or of a high-voltage terminal, are highly undesirable.Open gaps are also undesirable because of the risk of being bridged bysnow or sleet, or by birds or small animals.

The principal object of the present invention is to provide a protectedtransformer in which a lightning arrester is mounted on the outside ofthe transformer tank in association with a highvoltage terminal bushing,and connected to the high-voltage lead of the transformer through aseries gap which is combined with a terminal device.

Another object of the invention is to provide means for mounting alightning-arrester on a transformer tank in association with ahigh-voltage terminal device and for connecting the arrester to theterminal through a series gap, the arrangement being such that the gapand terminal device are protected and, in effect, enclosed so that nolive parts are exposed and the danger of the gap being bridged issubstantially eliminated.

Other objects and advantages of the invention will be apparent from thefollowing detailed description, taken in connection with theaccompanying drawing, in which:

Figure 1 is a perspective view of a protected transformer embodying theinvention, and

Fig. 2 is a view on an enlarged scale, partly in elevation and partly invertical section, showing the details of the lightning arrester mountingand terminal bushing. f

The invention is shown in the drawing embodied in a transformercontained in a tank i closed by a cover 2. The transformer itself may beof any suitable type or construction, since the invention is applicableto transformers of any desired type or size or, in general, to anyenclosed electrical device. The tank may be provided with hangers 3 formounting the transformer on a pole or other support. The particulartransformer shown has an internal circuit breaker, for overcurrentprotection, with an operating handle 4 on the outside of the tank.High-voltage terminal bushings 5 for the leads from the highvoltagewinding of the transformer are mounted in the tank wall diametricallyopposite to each other. Suitable low-voltage terminal devices may alsobe mounted in the tank wall, between the high-voltage bushings, theseterminals not being visible in the drawing.

The two terminal bushings 5 are identical in construction andarrangement. As shown in Fig. 2, each terminal bushing 5 is mountedhorizontally in the side wall of the tank I and a lead 6 from thehigh-voltage winding of the transformer extends through the bushing andis connected to a terminal device 'l in the outer end of the bushing.Any suitable type of terminal device may be utilized, the particulardevice shown being a setscrew type terminal having an opening 8 forrcceiving a line lead and a .set-screw 9 for clamping a pressure pad l0against the line lead to effect positive electrical connection. The setscrew 9 is provided with a large insulating knob or handwheel l I foractuating the screw, the knob Il being large enough to substantiallycover and close the open end of the bushing 5. Slots I2 are formed oneach side of the bushingopposite the terminal device 1 for entrance ofthe' line lead. The bushing l also has an opening or hole I3 formed inits lower side near the outer end of the bushing and opposite theterminal device 1 The terminal device 1 is provided with a. down-iwardly extending conducting member I4, which may be a threaded studthreaded into the lower side of the terminal device 1, and which extendsdown through the opening Il to form one electrode of a spark gap. ashereinafter described. Ihe member I4 also serves to prevent the terminaldevice 1 from being rotated when the knob II is turned to tighten orrelease a line lead.

The transformer is protected against lightning surges, or otherovervoltages, by means of a' lightning arrester I5 connected betweeneach of the high-voltage leads and ground. While only one arrester I5 isvisible in Figure l, it will be understood that a similar arrester,similarly arranged, is associated with the bushing 5 on the oppositeside of the tank. Any' suitable type of lightning arrester may beutilized, the particular arrester shown being an expulsion lightningarrester of the type disclosed and claimed in our copending applicationSerial No. 788,370, filed November 28, 1941, now Patent No. 2,546,006,issued March 20, 1951, and assigned toWestinghouse Electric Corporation.The arrester I5 is enclosed in a porcelair` housing I6 and comprises atube I1 of hard fiber, or other suitable insulating material capable ofevolving substantially un-ionized gas when subjected to the heat of anelectric arc. An upper electrode I8 is secured in the upper end of thetube I1, and a metal cap I8 closes the top of the tube. A metal stud 20is secured in the cap I8 and extends up through the top of the porcelainhousing I6 to form an upper terminal member for the arrester. A capmember 2I may be placed around the stud 28 on the outside of thearrester with a gasket to seal the housing and prevent the entrance ofmoisture. A hollow lower metal electrode member 22 extends from thelower part of the tube I1 through the bottom of the housing I6 and isthreaded to facilitate mounting the arrester. A loose stack ofalternating fiber disks 23 and fiber washers 24 is placed in the tube I1between the electrodes to restrict the arc path and to provideadditional gas-evolving material.

. In the operation of the arrester I5, when a lightning surge occurs, anarc is formed between the electrodes I8 and 22 in the restricted annularspace between the tube I1 and the stack of disks 23 and washers 24. Theheat. of the arc causes a large volume of un-ionized gas to be evolved.which is expelled in a blast through the hollow lower electrode 22, andwhich deionizes the arc path and blows out the arc to interrupt thepower current which tends to follow the surge. The gas also flowsthrough grooves 25 in the disks 23 into the central spaces of thewashers 24, the discs and washers being free to move apart axially torelieve the gas pressure without affecting the restriction of the arcpath, thus preventing the development of excessively high gas pressureswithin the arrester.

'Ihe lightning arrester I5 is mounted on a metal angle bracket 26 whichmay be of any suitable construction.- The threaded lower electrode 22 isthreaded into the horizontal portion of the bracket 28 and secured inposition by a nut 21 and cooperating lock washer. The bracket 26 alsohas a vertical portion which is bolted to the wall ci' the tank I bymeans of bolts 28 threaded into the tank, thus connecting the lowerelectrode 22 of the arrester to the tank I, which is usually grounded.The bolts 28 pass through elongated slots 23 in the bracket 28 so thatthe arrester is adjustable in vertical position.

It will be noted from the drawing that the bracket 28 is bolted to thetank directly below the terminal bushing 5 and is arranged so that thearrester Il is directly below the outer end of the bushing with itsupper terminal member 20 disposed opposite the opening I3 in the bushingand adjacent the lower end of the conducting member I4, so that theconducting member I4 and the upper terminal 28 of the lightning arresterform the electrodes of a spark gap between the arrester I 5 and theterminal device 1. The length of this spark gap may be adjusted bymoving the arrester Il vertically before the bolts 28 are tightened,this movement being permitted by the elongated slots 29. When the gaphas been adjusted to the desired length, the bolts 28 are tightened tohold the arrester in that position, and the bracket 26 is preferablylocked in place by a locking plate 30 through which the bolts 28 passand which extends vertically to the lower end of the bracket where it isbent over to prevent relative movement between the bolts and thebracket. Thus, a relatively simple means is provided for adjusting theposition of the arrester to determine the length of the spark gap, andsince the arrester and bushing are mounted on the same rigid surface,the adjustment will be maintained unchanged. It will be apparent thatother suitable adjusting means might be used, such as turning thearrester in the threaded mounting bracket, or any other suitable means.

It will be seen that the lightning arrester I5 is connected to thehigh-voltage terminal 1 of the transformer through a series spark gap,one electrode oi which is part of the terminal device itself, so thatthe gap is combined with the terminal. It is to be noted that theposition of the conducting member I4, which extends down through theopening I3 towards the upper terminal 2l) of the arrester, is such thatthe gap between the members I4 and 20 is protected and, in effect,enclosed, and that the terminal device 1 itself is enclosed in the endof the bushing 5, so that no live parts are exposed in a position whereaccidental contact could easily be made. The position and arrangement ofthe gap are also such that any risk of the gap being bridged issubstantially eliminated.

It should now be apparent that an improved mounting and arrangement of alightning arrester and high-voltage terminal device for protectedtransformers have been provided, by means of which the arrester isconnected to the high-voltage terminal through a series spark gap whichis combined with the terminal and which is protected and enclosed. Aspeciiic embodiment of the invention has been shown and described forthe purpose of illustration, but it will be apparent that various otherembodiments and modifications are possible. Thus, the terminal bushingand arrester may be mounted in any desired position on the tank,including the cover. Any suitable type of terminal device may be used,and the conducting member extending from it to form one electrode of thegap may take any suitable physical form, such as a projection formedintegral with the terminal device, or any other equivalent construction.Similarly, any suitable type of lightning arrester may be used, and thedetails of mounting the arrester on the tank and providing for verticaladjustment may be modiiled in any desired manner. It is to beunderstood, therefore, that although a particular construction has beenshown and described, the invention is not limited to this specificarrangement, but in its broadest aspects it includes all equivalenternbodiments and modicatons which come within the scope of the appendedclaim.

We claim as our invention:

In combination, a tank for an enclosed electrical device, a one-piece,integral, insulating terminal bushing mounted horizontally in a wall ofsaid tank, said bushing having a hollow therein and being open at theouter end, a terminal device mounted within the bushing in said hollow,said terminal device having an operating knob of insulating materialoutside the bushing and extending over the open outer end thereof tosubstantially completely enclose the terminal device, the terminaldevice being of a type which is liable to rotational movement in thebushing when said knob is operated, the bushing having an opening in thelower side thereof near the outer end of the bushing, a conductingmember on the terminai device extending downward therefrom into saidopening in position to engage a side o! the opening to prevent rotationof the terminal device, a lightning arrester, means for mounting saidlightning arrester below the bushing in a vertical position, thelightning rester having a terminal member at its upper end substantiallyin vertical alignment with said conducting member, and said mountingmeans including means for adjusting the position of the lightningarrester vertically to space the terminal member of the arrester adesired distance from said conducting member to form a spark gaptherewith.

imam. G. LEONARD. GUY Y. miem REFERENCES crrnn The following referencesare of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,018,672 Hill Oct. 29, 19352,029,140 Treanor Jan. 28, 1936

